Mechanical relay of the fluid jet type



Oct. 1, 1946. I K, TODD' 2,408,705

MECHANICAL RELAY OF THE FLUID JET TYPE Filed Dec. 31, 1943.

2d. FIG. 3.

' INVENTOR KEITH" WATSON Tom) ATTORNEYS Patented Oct. 1, 1946 KeithWatson Todd, Warrington, England, assignor to Metropolitan-VickersElectrical Company Limited, London, England, a company of Great BritainApplication December 31, 1943, Serial No. 516,595.

In Great Britain May 28, 1940, and September 1 3 Claims.

This invention relates to mechanical relays of the fluid jet type.

A relay of the type referred to comprises a nozzle to which air or otherfluid is continuously supplied, usually at constant pressure, and anorifice, which may be the opening to a second nozzle, which orificereceives fluid from the jet issuing from the aforesaid nozzle. Thenozzle and orifice are usually enclosed in a casing having an outletport andsometimes provided with means whereby the pressure within thecasing may be controlled, for instance maintained above or at or belowatmospheric pressure. The fluid received in the receiving orifice mayact upon a piston or bellows member for effecting some indicating orcontrol operation in accordance with the control imposed upon the relay,this control in the present instance being effected by Varying thedegree of impingement of the jet upon thereceiving orifice. Heretoforewhen this method of control has been employed the nozzle and receivingorifice have been maintained as far as practicably possible in coaxialalignment when in one control position, the axis ofthe receiving orificebeing taken, in this connection and in the following, as the axis of thereceiving nozzle if present (including a receiving perforation if thelength thereof permits the assignment of an axis) or the normal to theplane face of the receiving orifice if no receiving nozzle is employed.I 7

However, it has been found that-with this-a rangement, under certainconditions considerable pulsations of the received pressure occurirrespectiveof the separation of nozzle and receiving orifice over aconsiderable range, even although precautions are taken to maintainuniformity of the pressure in the transmitting nozzle. These pulsationsmay also vary in amplitude and become considerable in parts of theseparation range.

In relays as above set forth the method of control used may effect thesaid change in degree of impingement in any of various ways such as bydeflection of the one axis relatively to the other about any suitablecentre and whether retaining a coplanar relationship of the axes or not,by movement apart of the two orifices along any line but preferablyalong the axis of the first or outlet nozzle, or by deflection of thejet by employed such methods of control other than bymeans of a materialvane arranged to intercept the stream flow.

According to the present invention, with a view to avoiding orminimising pressure pulsations as above mentioned, in relays of the typereferred to controlled otherwise than by a material vane, interceptingthe stream flow, the transmitting nozzle and receiving orifice arearranged so that in no control position do their axes subtend withrespect to one another an angle of less than 5 from coaxial alignment,and that inat least one control position the axis of the transmittingnozzle to which the pressure fluid is supplied passes within the area ofthe receiving orifice. In experimental use of one system of nozzles itwas found desirable for the angle between the axes to exceed 20.

Factors affecting the amplitude of the, received pressure pulsations,and hence the angle necessitated between the axes of the nozzle andreceiving orifice for the removal wholly or mainly of said pulsations,are the absolute and relative sizes of the bores of the nozzle andreceiving orifice, the shape of the orifices, their distance apart, thenature of the fluid medium used, the transmitting jet pressure and thepressure of the medium surrounding the jet. 7

With a relayof the type referred to when the fluid used by the jets is arelatively highly compressible one, such as air, certain irregularitiesappear to arise which it is believed are dependent upon the air velocitybeing at least in the neigh bourhood of the velocity of the propagationof sound. It is known that under these conditions the stream of fluidbeyond the transmitting nozzle may enter into a condition of standingwaves, and that the length between nodes'will depend upon the ratio ofpressure of supply to that of the fluid medium surrounding the jets,whilst there is a complicated structure within this jet and certainregions of abrupt change known as Riemann lines. It is also know thatbeyond the Riemann line the jet conditions may change and cease to beperiodic, becoming somewhat indeterminate. Considerable experimentalinvestigation has been made on these jets by optical methols along thelines of investigation made by Julius Haitmanri-seeIngeniorvidenskabelige Slq'ifter 1939, Nr.- 4. These investigations havetended to confirm the aforesaid assumptions, and have led to the presentinvention whereby one source of irregularity in the receiving pressureof the relay can be avoided or minimised.

Therefore, according to a subsidiary feature of thepresent invention theoccurrence of the Riemann line isprevented or substantially prevented bythe use of a convergent-divergent nozzle for the transmitter of therelay. In the said experimental investigations the shape of thereceiving nozzle has not been altered; it has been very slightlyconvergent towards the entrance orifice.

While the use of a convergent-divergent transmitting nozzle has beenfound very effective it has been found that there are still certainpulsations in the receiving pressure to be dealt with and according to afurther subsidiary feature of the invention these smaller pulsations ordisturbances are controlled by the introduction of a wire or wires or awire grid across the surface of the receiving nozzle. There may be asingle wire of diameter about one-tenth that of the orifice placeddiametrically across the latter. Alternatively a series of parallelwires may be used. It will be appreciated that the presence of severalwires unavoidably reduces the available receivin pressure.

The invention will now be described with reference to the accompanyingsomewhat diagrammatic drawing in which:

Fig. 1 is a perspective view of a fluid jet rela in accordance with theinvention,

Fig. 2 being an enlarged sectional view of part of the transmittingnozzle of the relay, and

Fig. 3 being an enlarged perspective view, partly in section, of thereceiving nozzle with fitted mesh diffuser.

In Figure 1, l and 2 are nozzles respectively supported on arms 3a and32) forming parts of a fixed frame mounting 3. The nozzle I has attachedto it, at its rear or anchored end, a nipple 4 to which will beconnected a pipe for conveying workin fluid, for example air, underconstant pressure to the interior of the nozzle. This nozzle constitutesthe transmitting nozzle and has a through bore la which, at the outletend, is of convergent-divergent form as illustrated more clearly in Fig.2. The nozzle 2, intended to receive the fluid ejected under pressurefrom the transmitting nozzle I and herein referred to as the receivingnozzle, has a through bore comprising a cylindrical part 2a and areduced cylindrical part 21).

Supported in the frame 3 is a cylinder 5 in which is disposed a piston 6attached at its front face to a rod 60. and at the rear face to rod 6b;the rods 6a and Eli extend through substantially pressure-tight sealingglands mounted in the closed opposite ends of the cylinder "5. The boreId. of the transmitting nozzle I registers with a duct 3a in thesupporting arm 3a whereby, when pressure fluid is supplied to thetransmitting nozzle- I, pressure fluid is also supplied to the trappedspace 5a of cylinder 5 accordingly to act upon the piston 6. The bore 2aof the receiving nozzle registers with a duct 3b in the supporting arm31) whereby pressure fluid received by the nozzle 2 from thetransmitting nozzle 1 is fed into the trapped space 5b in cylinder 5accordingly to act upon the piston 6.

At 1 is shown a third nozzle which, in the example illustrated, issupported by a bracket la attached to a frame lb and is, in turn,supplied with fluid under constant pressure through pipe 8, thereby toprovide a fluid jet acting substantially at right angles to the fluidjet passing between the nozzles l and 2, The frame 11) to which thenozzle 1 is attached comprises a pair of parallel levers 1c and 7dpivotally connected at their respective ends to a link Fe extending fromthe bracket la and to a link if, and is supported on a knife edge 9aintermediately of a beam 9 which, at one. end, is supported on a knifeedge 3c forming part of the frame 3 and at the other end is pivoted to arod ID to which initiating movement will be imparted when the relay isintended to operate. Attached to the link 1] of the frame lb is a rod Hwhich rests at its free end on a cam !2 which is attached to anextension of the piston rod 5b projecting beyond the supporting arm 3b.

With the arrangement described, and assuming that the normal position ofthe jet from nozzle 1 is such that said jet partially interferes withthe under-side of the jet from nozzle l then, when the rod Ill is forexample depressed, pivot 9a for the frame lb will be lowered accordinglyto depress nozzle 1 and correspondingly reduce the extent to which thejet from nozzle I is interfered with by the control fluid jet fromnozzle 1, so that the pressure in the receiving nozzle 2 is raised andthe pressure in the trapped space 5b of the working cylinder 5correspondingly increased relatively to the constant opposing pressure,in the trapped space 5a, with the result that the piston 6 will be movedto the left in the drawing. With such movement of piston 6, the at.-tached piston rod 6a is moved outwardly from the working cylinder 5accordingly to operate mechanism with which the relay will beassociated, and at the same time, the piston rod 81) is movedaccordingly, thereby retracting the cam I2 and permitting downwardmovement of the rod H, and causing the frame 111 to swing about. pivot9a. in the direction to raise the nozzle 1 to its normal positionaforesaid, and so restoring the jet from. said nozzle 1 to the positionin which it partially interferes with the under-side of the jet fromnozzle l. Similarly, for an upward movement of the rod Iii, piston 6will be moved to the right in the drawing accordingly, through piston,rod 60., to operate the mechanism associated with the relay, and,through the rod 6b, to operate the cam l2 and rod H to rock the frame Tbabout pivot Ea for restoring the nozzle 1, and thus the control jettherefrom, to its normal position aforesaid.

If it were desired-that mechanism similar to that illustrated shouldrespond when a control fluid jet ejected from nozzle 1 is moved from anormal position in which said jet interferes with the upper-side of thejet from nozzle I, then the only change which would be required in themechanism to ensure restoration of the control jet from nozzle 1 to itsnormal position in relation to the jet from, nozzle 1 would be for thecam 12 to be reversed, namely, so that its inclined surface is directedupwardly from the left toright in the drawing.

It is preferable that the transmitting nozzle l and the receiving nozzle2 are arranged so that the maximum pressure receivable through nozzle 2in the trapped space 522 is approximately half the normal constantpressure in the trapped space 5a and that the amount of interference ofthe control jet from nozzle 1 on the jet from nozzle l is such that thenormal received pressure in trapped space 5b is about half the maximumavailable pressure, that is, about a quarter of the normal constantpressure in the trapped space 5a.

Despite this dissimilarity in pressure on. either side of the piston 6,the differential areas are such that a balance condition is maintained.

Advantageously, the design of. the orifice in the control jet nozzle 1is such that it is not possible for over-movement of the rod. H). toresult in such movement of the control jet from nozzle 1 that itsinfluence upon the jet from nozzle I is entirely removed.

As shown in Fig. 3, the receiving nozzle 2 is fitted at its outer endwith a cylindrical part 20 having an attached'circumferential flange 2dfor supporting a wire grid 26 of relatively fine mesh in a planesubstantially at right angles to the axis of the nozzle, to act as adifiuser for said receiving nozzle for the purpose hereinbeforedescribed.

As represented in Fig. 1, the transmitting and receiving nozzles I and 2respectively are mounted so that their axes are not in linear alignmentbut are inclined to one another at an angle or, which angle, for allworking positions, has a value which exceeds 5 and which willgenerallybe in excess of 20. Moreover, as represented in the drawing, the axis ofthe transmittin nozzle I will generally pass within the area of theinlet end of the receiving nozzle 2.

I claim:

1. A fluid-jet relay comprising a transmitting nozzle adapted to besupplied with pressure fluid, an orifice for receiving the fluid jetfrom the transmitting nozzle, a controlling nozzle for directingpressure fluid transversely of the jet from the transmitting nozzle,means responsively 0perable to a control influence for varying theinclination of incidence of the transverse jet with the jet from thetransmitting nozzle, means responsive to pressure fluid received by thereceiving orifice for rendering available an influence representative ofsaid control influence, said transmitting nozzle and receiving nozzlebeing arranged with the axis of the transmitting nozzle passing throughthe area of the receiving nozzle and inclined to the axis of thereceiving orifice so as to subtend therewith an angle of at least fivedegrees from coaxial alignment.

2. A fluid-jet relay comprisinga transmitting nozzle adapted to besupplied with fluid at constant pressure and a receiving nozzle arrangedwith the axis of the transmitting nozzle passing through the area of thereceiving nozzle and inclined to the axis of the receiving nozzle so asto subtend therewith an angle of at least five degrees from coaxialalignment, a control nozzle for directing fluid at constant pressuretransversely of the jet from the transmitting nozzle, means responsivelyoperable to a control influence .for varying the inclination ofincidence of the transverse jet With the jet from the transmittingnozzle, a pressure-responsive servo-piston, together with means forsupplying fluid at the pressure in the transmitting nozzle to one faceof said servo-piston and means for supplying pressure 1 fluid receivedin the receiving nozzle to the opposite face of said servo piston.

3. A fluid jet relay comprising a transmitting nozzle adapted to besupplied with fluid at constant pressure, nozzle for receiving fluidemitted from the transmitting nozzle, a controlling nozzle for directingfluid at constant pressure transversely of the emission from thetransmitting nozzle, means responsively operable to a variable controlinfluence for correspondingly varying the angle of incidence between thetransverse fluid emission and the fluid emission from the transmittingnozzle, means continuously responsive to the difference between thepressure in the transmitting nozzle and the pressure in the receivingnozzle for rendering available an influence which is at all timessubstantially representative in magnitude of said control influence,said transmitting nozzle and receiving nozzle being arranged so that theaxis of the transmitting nozzlepasses through the area of the receivingnozzle and is inclined to the axis of the receiving nozzle so as tosubtend therewith an angle of at least five degrees from coaxialalignment.

KEITH WATSON TODD.

